1. Field of the Invention
The present invention relates generally relates to an apparatus and method for determining the position of a moving component and more particularly to a single channel encoder.
2. Description of the Prior Art
Generally, the process of electrophotographic printing includes charging a photoconductive member to a substantially uniform potential so as to sensitize the surface thereof. The charged surface of the photoconductive surface may be exposed to a light image of an original document to record an electrostatic latent image on the photoconductive member, the latent image corresponding to the informational areas contained in the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a toner material, such as a suitable powder or liquid, into contact with the photoconductive member. A toner image is formed on the photoconductive member, which toner image is subsequently the photoconductive member, which toner image is subsequently transferred to a support member. Finally, the toner image is heated for fusing it permanently to the support member in image configuration.
In a typical electrophotographic printing machine a plurality of processing stations are positioned about the photoconductive member. Furthermore, other processing stations are located in the path of the copy sheet. These processing stations perform all of the operations necessary to insure that a completed copy of an original document is generated. Each processing station is energized at a selected time during the operating cycle. This is achieved by a timing pulse generator associated with the photoconductive member.
In one example, the timing pulse generator comprises a disk coupled with the photoconductive member, the disk having a plurality of spaced apart marks thereon. The marks are arranged on the disk so that the marks can rotate with the photoconductive drum when the disk is rotatably mounted therewith. Each mark serves as a position indicator for timing the operations in the printing machine. The timing pulse generator further comprises a light source and a photodetector, both of which can be respectively disposed on opposing sides of the disk to sense the passage of the marks. In this way, a pulse is generated for each increment between adjacent marks of the disk. These pulses are transmitted to a control system for actuating one of the processing stations at an appropriate time to permit the formation of a copy of the original document on the support member.
When using the disk in a rotary encoder arrangement, it is desirable to generate an index pulse upon each revolution of the disk for indicating a point of origin of the disk. With this origin, the angular position of the disk, and thus the angular position of a moving component, such as the photoconductive member, can be determined readily. The following patent discloses a rotary encoder in which such an index pulse is generated:
U.S. Pat. No. 4,233,592; Patentee: Leichie; issued Nov. 11, 1980 PA1 U.S. Pat. No. 4,786,803; Patentee: Majette et al.; Issued Nov. 22, 1988 PA1 U.S. Pat. No. 4,025,186; Patentee: Hunt, Jr. et al; Issued: May 24,1977
U.S. Pat.No. 4,233,592 discloses an angular position detecting apparatus which provides an absolute position reference by detecting a "missing tooth" in a notched disk. In operation, a positioned sensor detects the passage of teeth on the rotating notched disk and generates a corresponding output signal in the form of a pulse train. The missing tooth in the disk creates a gap or delay int he pulse train output as it passes by the positioned sensor. That gap or delay can be detected by a circuit comprising a Schmidt trigger and monostable multivibrator detecting circuit for determining an absolute reference position of the disk.
The following patents relate to linear, single channel encoders which are capable of generating information regarding the position of a moving sensor head relative to a strip having counting and reference pulses disposed thereon:
U.S. Pat. No. 4,789,874; Patentee: Majette et al.; Issued Dec. 6, 1988
U.S. Pat. No. 4,786,803 discloses a single channel encoder system that controls the movement of an ink jet print head by detecting a reference position marking on an encoder strip. A detector reads several wide bands located on a strip of regularly-spaced narrow scale lines to generate a pulsed signal output indicative of a reference position for the print head.
U.S. Pat. No. 4,789,874 discloses a single channel encoder system that controls the carriage position and movement of an ink jet pen relative to the detection of an irregular delay in a pulsed signal output. In operation, a detector reads a pattern of closely-spaced narrow print bands on an encoder strip and converts the pattern into a logic output signal. A wide band on the encoder strip generates a corresponding irregular delay in the output signal, which delay can be detected to provide a position reference for controlling the movement of the ink jet pen.
A dual encoder arrangement adapted for use with a photoconductive member is disclosed in the following patent:
While the wide bands of the Majette et al. patents serve to indicate the position of the print head or pen relative to the encoder strip, the wide bands cannot be counted as timing pulses. That is, during the period in which the detector is being passed over one of the wide bands, the count of the timing pulses must be halted. Thus, the wide bands cannot be used to generate both timing pulses and reference pulses. Similarly, the missing tooth of the Leichle patent is not intended for use as a timing pulse. Indeed, Leichle discloses a circuit specifically devised to reconstitute the timing pulse lost as a result of using the missing tooth. It would be desirable to provide a single channel encoder possessing a reference pulse that can be employed as both a timing pulse and a position indicating pulse.